The sirens are generally controlled by county dispatchers. They are designed to alert people outdoors to a threat — whether it’s a chemical spill, a problem at the nuclear power plant or more likely, something to do with the weather.

Most metro counties activate them when the National Weather Service issues either a tornado warning or a severe thunderstorm warning with winds forecast to exceed 70 miles per hour.

But Dakota County activates its sirens for every severe thunderstorm warning, even those with lower wind speeds.

“At 60 miles per hour, you start to have branches coming off trees. You have small trees falling over that can bring down power lines,” Emergency Preparedness Coordinator David Gisch said.

But unlike Ramsey County, Dakota doesn’t have to blow all the horns countywide. It can target individual cities, which cuts down on the potential for false alarms. Scott, Hennepin and Carver County have that ability, too. And Washington County has two warning zones divided by Highway 36.

Anoka County did not respond to an inquiry about its warning siren policies and capabilities.

Shameless plug: we did a project on whether the Twin Cities is prepared for a major storm. Check it out here.